Fix pa_main_volume_policy lifecycle handling
Fix pa_main_volume_policy lifecycle handling

We should call pa_main_volume_policy_get() only once during module
initialization, and then call pa_main_volume_policy_unref() when the
module is unloaded.

Change-Id: I5c482822dff683a79127812c9948eff711ae9066

otcshare/pulseaudio-module-murphy-ivi,otcshare/pulseaudio-module-murphy-ivi,otcshare/pulseaudio-module-murphy-ivi,otcshare/pulseaudio-module-murphy-ivi